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What is Viagra used for?
This FDA approved prescription medicine is used to
treat impotence in men. The product increases the body's ability to achieve and maintain an
erection during sexual stimulation.

This drug does not protect you from getting sexually
transmitted diseases, including HIV.

Who should not take the drug?
Men who are currently using medicines that contain nitrates, such as nitroglycerin should
not use the drug because, taken together, they can lower the blood pressure too much.

The product should not be used by women or children.

General Precautions with Viagra: You should have a complete medical history and exam to determine the cause of
your impotence before taking the product.

Men who have medical conditions that may
cause a sustained erection such as sickle cell anemia, leukemia or multiple myeloma or who
have an abnormally shaped penis may not be able to take the drug.

There are several
medications that are known to interact with the drug, so be sure to tell your doctor about
all medications you are taking including those you can get without a prescription.

The medicine has not been studied with other treatments for impotence, so use in
combination with other treatments is
not recommended.

How should I take Viagra? Your healthcare provider may prescribe the product as one tablet once a day,
about 1 hour before sexual activity. However, the product may be taken anywhere from 30
minutes to 4 hours before sexual activity.

What are some possible side effects of Viagra? (This list is NOT a complete list of side effects reported with the drug. Your
healthcare provider can discuss with you a more complete list of side effects.)

The
medicine is generally well tolerated. If any side effects are experienced, they are
usually mild and temporary.

Using Viagra with other MedicinesAlways discuss with your health care practitioner ALL of the medications you are
taking (prescription and over-the-counter). In that way, you can receive the best advice
for your own situation.

At present, the drug is not recommended for people taking commonly
prescribed short- and long-acting nitrates because the combination may lower blood
pressure.

The
mechanism of action of Sildenafil citrate
involves the release of nitric oxide (NO) in the
corpus cavernosum of the penis.

NO binds to
the receptors of the enzyme guanylate cyclase
which results in increased levels of cyclic
guanosine monophosphate (cGMP), leading to
smooth muscle relaxation (vasodilation) of the
intimal cushions of the helicine arteries,
resulting in increased inflow of blood and an
erection.

Sildenafil is
a potent and selective inhibitor of cGMP
specific phosphodiesterase type 5 (PDE5)
which is responsible for degradation of cGMP in
the corpus cavernosum.

The molecular
structure of sildenafil is similar to that of
cGMP and acts as a competitive binding agent of
PDE5 in the corpus cavernosum, resulting in more
cGMP and better erections.[

Without
sexual stimulation, and therefore lack of
activation of the NO/cGMP system, sildenafil
should not cause an erection. O

ther drugs
that operate by the same mechanism include
tadalafil (Cialis) and vardenafil (Levitra).

Sildenafil is
metabolised by liver enzymes and excreted by
both the liver and kidneys.

If taken with
a high-fat meal, absorption is reduced; the time
taken to reach the maximum plasma concentration
increases by around one hour, and the maximum
concentration itself is decreased by nearly
one-third.

The
primary indication of sildenafil
is treatment of erectile
dysfunction (inability to
sustain a satisfactory erection
to complete intercourse). It use
is now standard treatment for
erectile dysfunction in all
settings, including diabetes.

People on
antidepressants may experience
sexual dysfunction, either as a
result of their illness or as a
result of their treatment.

A 2003 study
showed that sildenafil improved
sexual function in men in this
situation.

Following up
to earlier reports from 1999,
the same researchers found that
sildenafil was able to improve
sexual function in female
patients on antidepressants as
well.

Professional sports players
have been using drugs such as
Viagra thinking that the opening
of their blood vessels will
enrich their muscles, therefore
enhancing their performance.

Viagra's
popularity with young adults has
increased over the years.

It is
sometimes used recreationally,
though this use is somewhat
pointless in young, healthy men,
as they receive no benefit from
the drug.

Some users
mix Viagra with
methylenedioxymethamphetamine (MDMA,
ecstasy) or other stimulants in
an attempt to compensate for the
side effect common to many
amphetamines of erectile
dysfunction, a combination known
as "sextasy", "rockin' and
rollin'", or 'trail mix'."
Mixing with amyl nitrite is
particularly dangerous, and is
potentially fatal.

A
low-concentration solution of
sildenafil in water
significantly prolongs the time
before cut flowers wilt; one
experiment showed a doubling in
time from one week to two weeks.

The mechanism
of action is similar to that in
humans: nitric oxide leads to
the production of cGMP whose
degradation by PDE5 is inhibited
by sildenafil.

The 2007 Ig
Nobel Prize in Aviation went to
Patricia V. Agostino, Santiago
A. Plano and Diego A. Golombek
of Universidad Nacional de
Quilmes, Argentina, for their
discovery that Viagra aids
jet lag recovery in
hamsters. Their research was
published in the Proceedings of
the National Academy of Sciences.

DOSAGE

Viagra Pfizer
pills are blue and
diamond-shaped with the words
"Pfizer" engraved on one side,
and "VGR xx" (where xx stands
for "25", "50" or "100", the
dose of that pill in milligrams)
engraved on the other. The dose
of sildenafil for erectile
dysfunction is 25 mg to 100 mg
taken not more than once per day
between 30 minutes and 4 hours
prior to sexual intercourse.

Some
complained of blurriness and loss of peripheral
vision. In July 2005, the U.S. Food and Drug
Administration found that sildenafil could lead
to vision impairment in rare cases and a number
of studies have linked sildenafil use with
nonarteritic anterior ischemic optic neuropathy.

As a result
of these postmarketing reports, in October 2007,
the FDA announced that the labeling for all PDE5
inhibitors, including sildenafil, required a
more prominent warning of the potential risk of
sudden hearing loss.

HISTORY

Sildenafil (compound
UK-92,480) was synthesized by a group of pharmaceutical chemists
working at Pfizer's Sandwich, Kent, research facility in
England.

It was initially studied for
use in hypertension (high blood pressure) and angina pectoris (a
symptom of ischaemic heart disease).

The first clinical trials
were conducted in Morriston Hospital in Swansea.

Phase I clinical trials under
the direction of Ian Osterloh suggested that the drug had little
effect on angina, but that it could induce marked penile
erections.

Pfizer therefore decided to
market it for erectile dysfunction, rather than for angina.

The drug was patented in
1996, approved for use in erectile dysfunction by the US Food
and Drug Administration on March 27, 1998, becoming the first
oral treatment approved to treat erectile dysfunction in the
United States, and offered for sale in the United States later
that year.

It soon became a great
success: annual sales of Viagra in the period 19992001 exceeded
$1 billion!

The British press portrayed
Peter Dunn and Albert Wood as the inventors of the drug, a claim
which Pfizer disputes. Their names are on the manufacturing
patent application drug, but Pfizer claims this is only for
convenience.

Even though sildenafil is
available only by prescription from a doctor, it was advertised
directly to consumers on U.S. TV (famously being endorsed by
former United States Senator Bob Dole and soccer star Pel้).

The "Viagra" name has become
so well known that many fake aphrodisiacs now call themselves "herbal
Viagra" or are presented as blue tablets imitating the shape and
colour of Pfizer's product.

Viagra is also informally
known as "Vitamin V", "the Blue Pill", as well as various other
nicknames.

By 2007, Viagra's global
share had plunged to about 50 percent due to several factors,
including the entry of Cialis and Levitra, along with several
other counterfeits and clones, and reports of vision loss in
people taking PDE5 inhibitors.

In February 2007, it was
announced that Boots the Chemist would trial over the counter
sales of Viagra in stores in Manchester, England.

Men aged between 30 and 65
would be eligible to buy four tablets after a consultation with
a pharmacist.

Pfizer's worldwide patents on
sildenafil citrate will expire in 20112013.

The UK patent held by Pfizer
on the use of PDE5 inhibitors as treatment of impotence was
invalidated in 2000 because of obviousness; this decision was
upheld on appeal in 2002.

CHEMICAL SYNTHESIS

The preparation steps for synthesis of Viagra
(sildenafil citrate) are as follows: